The most important event in the Iowa presidential campaign this week actually takes place in Texas, where Republican presidential candidate Mitt Romney will address his faith and how it would inform his presidency. Many are comparing this moment to John F. Kennedy's 1960 campaign speech - also in Texas - in which he put to rest concerns about whether a Catholic could serve as president. But every aspect of Romney's speech - from how campaigns run, to voters' expectations about religion, to Mormonism itself - reminds us that, unfortunately for Romney, this is no John Kennedy moment.

First is the matter of timing. Kennedy's speech came late in the game, mere weeks before the 1960 general election. Kennedy was not one of a dozen candidates vying for his party's nomination, but was the Democratic nominee running a strong campaign. Therefore his purpose was to clear the air and provide assurances that, as a Catholic, he could be independent of his church and make policy decisions on their own merits. As he wisely put it, "I am not the Catholic candidate for president. I am the Democratic Party's candidate for president who also happens to be a Catholic."

All signs are that Romney, a Mormon, knew he had to answer similar questions, but preferred to do so, as Kennedy did, later in the campaign. The tough issues are best faced when you already have momentum and are merely clearing the path of any obstacle that might keep interested people from voting for you. To do this too early - before people are focused, when voters aren't sure about your religion or what it means - raises a tough issue without disposing of it. But the surprising move of Southern Baptist minister Mike Huckabee into the frontrunner spot in Iowa has changed the political calculus and the timing.

Not only is the timing of Romney's speech different, but so must be its purpose and approach. In a Republican primary in 2008, Romney's target audience does not want to hear Kennedy's message that his religion isn't going to get in the way. In fact, evangelical Christians - who now make up a very active 30 percent of the GOP voting base - are listening for a very different message, namely that a candidate's religion does matter, and that it leads him to particular positions on abortion and other social issues. This speech can't merely play defense against religious discrimination - as Kennedy did, but actually needs to win votes from evangelicals who are now moving toward Huckabee.

This leaves Romney with a Mormonism problem different from what most people are talking about. Yes, there is the general unease people have about some of the particularities of Mormonism. Yes, it is a problem that some Christians consider Mormonism a cult or not Christian, because it believes in revelations that follow the time of Christ. But those are Kennedy-like questions Romney could probably handle if he gets traction and wins the Republican nomination. The more immediate challenge - in the Republican primaries - is that Romney, like many Mormons, thinks of his faith more in terms of values and lifestyle and less about it as a guide to political positions.

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Romney will doubtless give a good speech that mainstream Americans - who want their leaders to be religious in terms of values but not too religious on particular issues - can accept. Unfortunately for Romney, that's not the issue now. It's how to reach those evangelical Christians who have energized the Republican base and who want more from their candidates' religion than family values.

Richard Nixon, a masterful campaigner, used to say that in the Republican primaries he had to run to the right, then in the general election he needed to switch gears and run toward the middle to win. Romney's speech will run toward the center, which is the speech he needs to give next October. But he will not make it to October, if he can't first satisfy evangelical Christians in Republican primaries such as Iowa.

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